TM 5-4310-362-14
PRESSURE SWITCH UNLOADER (MODEL 20-911)
The pressure switch unloader releases pressure from the high pressure cylinder of the compressor when the electric
motor stops.
The electric motor draws more current when it is first starting up than when it is running at full speed. It also draws more
current when it works against a load such as compressing air as when it is running without a load. The unloader prevents
big current surges in the motor by unloading the compressor when the motor is stopped and during the first few cycles of
start up.
Here is how the unloader works: Lever B is attached to pressure switch diaphragm C. At the same time the diaphragm
moves to open switch contacts and stop the motor, it also causes lever B to push open valve A and release pressure from
the cylinder head.
When the pressure in the tank falls, the diaphragm C moves in the opposite direction closing switch contacts starting the
electric motor and at the same time causes lever B to close valve A and the compressor builds up pressure.
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